Unifi: Dead UAP-AC-PRO?
On my way to bed last night, I noticed that two of the smart devices in my office - the lamp and the shelving lighting - were both offline in Home Assistant. Strangely, the Skyfan wasn’t offline, so it took me a moment to figure out what the issue was: the Unifi access point that covers the rear portion of the house had decided to croak on me, and as they were unable to maintain a decent enough connection they were ushered off by the front one, never to be heard from again.
I spent far too long suspecting my patch cables (very cheap Temu things that I admittedly don’t really have any objective complaints about), I slipped a zip-tie under the AP to get it off the ceiling, and replaced it with a spare I had, which came right up. I adopted it, configured it correctly, and went to bed angry.
Over breakfast this morning I was having a read, and found a few threads mentioning a fairly wide-spread problem some 7 years ago, where Unifi were actually RMAing these devices outside of the warranty period, suggesting something they knew about, which was further irritating to me. Continuing my search, I found a reddit thread mention of devices where they failed to negotiate power-over-ethernet with a switch (exactly how mine were hooked up), so on my lunch break I dug out a POE injector and connected it up and yep - it came to life.
I started thinking about whether it’d be possible, or even worth it, to replace the IC responsible for this when I stumbled upon gold: someone’s not only been through this, but they successfully rescued the device by simply removing (not replacing) a single component!
I’ll replicate, tersely, the instructions here as I don’t trust Ubiquiti not to trash the thread - indeed I couldn’t find the linked instructions to open the fucking thing. But in case the thread disappears, the user TomBK on the Unifi community came to my rescue at least:
- Verify that the UAP does actually power up via a POE injector, you’re wasting your time if it doesn’t.
- Use a plastic spudger to pry it open. There are no screws, there’s five clips and a fuckload of adhesive holding it together. It took more force than you think, but once one clip pops the rest are trivial to undo.
- Remove the four screws to liberate the PCB from the back of the case.
- Flip the board over, and observe near the USB port. With the USB port oriented towards you, looking at the back side of the board, there is a line of four tiny transistors to the right, and then below it are two capacitors, C406 and C2. They may not be present, if they’re not, you’re wasting your time.
- Check the resistance of C2 - if it registers as a short or very low resistance, it’s probably cooked. If it’s open, this is probably not the fault that’s killed your UAP.
- Desolder C2 with a decent iron or soldering gun. It’s tiny, so I just used some flux, flooded the tip of the iron, heated it up and pushed it off. I then used more flux and a clean tip to make sure the pads are not bridged, and then verified no short with a multimeter.
- Plug the device into a switch and see if it powers on. If it doesn’t, this is probably not the issue that killed your UAP.
- Reassemble the device and put it back into service.
I’m not an electronics engineer, so I don’t know if the proposed explanation and solution are sound, but it’s worked for me.
As of the time of writing it’s not skipped a beat for 48 hours, so that’s alright.
